1. Field of the Invention
This invention relates in general to wireline operations during earth boring, and in particular to a wireline sealing apparatus and method for use with a wireline directional indicating instrument lowered within the drill string during directional drilling operations.
2. Description of the Prior Art
Many wells are directionally drilled, that is oriented at a given angle with respect to the vertical and in a designated direction. This technique is used frequently in offshore petroleum drilling, where up to sixty wells may be drilled from a single platform at angles of deviation up to about 58.degree.. Each well is drilled vertically to a selected depth, then the angle and direction of drilling is changed from time to time until the precise point is reached. One method of changing the orientation is to use a hydraulic drill bit which contains offset jets to cause the borehole to wear in a particular direction. Under this technique, the drill string is not rotated. An orienting or directional indicating instrument may be lowered into the drill string on a wireline to continuously indicate the direction and angle as the drill string advances. The directional signal can be monitored uphole while drilling. Once the desired orientation is achieved, which may take four or five stands of drill pipe, the drill string is pulled and a conventional drill bit is attached for conventional rotary drilling until the orientation is desired to be changed again.
In order to be able to circulate drilling fluid while the wireline instrument is located downhole within the drill string, conventionally a circulating head is placed at the top of the drill string, and a wireline pack-off is placed on top of the circulating head. Drilling fluid from the pumps is connected to the side of the circulating head. The wireline pack-off is a rubber element type having rams that squeeze the elements against the wireline to seal against the drilling fluid pressure and the drill string. When closed, the line may not be moved, otherwise the seal will be broken and grooves cut into the rubber elements. Normally, while the wireline instrument is being lowered into the well and being retrieved, since circulation can not be maintained simultaneously, the drill bit is positioned one joint off bottom to prevent sticking. Once the wireline instrument is in its proper position in the drill string, the pack-off is actuated, the drill string is lowered until the bit is on bottom and circulation resumed until the stand of drill pipe in the derrick is drilled down.
One disadvantage of this technique is that it has been impossible to entirely remove slack from the line. Due to the light weight of the wireline instrument, friction between the line and the drill string, and other factors, the lower portion of the wireline is under little tension and tends to coil. The upper portion of the wireline may be under satisfactory tension because of the weight of the wireline itself. However, there is little line weight near bottom and the instrument lacks sufficient weight itself to pull the lower portion, which may be several hundred feet or more, tight. Consequently, when drilling fluid circulation is started, the high and pulsating flow rate tends to whip the loose portions of the line, wearing and causing the line to kink and knot. When this occurs, considerable portions of the line have to be discarded.
Another disadvantage is that circulation must be interrupted when the wireline instrument is lowered and retrieved. In certain areas, interrupting circulation for the approximate twenty to thirty minutes required to run the line in or retrieve it can cause the drill pipe to stick in the borehole. The drill string must be lifted one joint from bottom while circulation is discontinued to reduce this possibility. Since this lifting occurs while the wireline is still rigged up and the wireline instrument is downhole, occasionally the wireline catches or snags in the drill rig derrick, kinking or breaking the line. This may mean that several thousand feet of line still downhole has to be discarded.
Wireline sealing devices that allow the line to be moved while the seal is maintained are known. These devices, known as "lubricators", contain a flow tube that fits closely about the line. Grease is injected into the flow tube under pressure to affect the seal. The lubricators are used in cased hole work, normally being connected to the production tubing so that the wireline instrument may be run in a well that is under flowing pressure or will be after the wireline operation. As far as is known, lubricators have not been connected to a drill string for open hole drilling operations, nor used in an arrangement wherein drilling fluid is pumped down from above. Also conventional lubricators extend upward a considerable distance from the connection with the tubing. Because of their height, they could not fit between the top of the drill string and the traveling blocks that suspend the drill string during open hole directional drilling operations.